Compact inward-firing premix fuel combustion system, and fluid heating system and packaged burner system including the same

ABSTRACT

An inward-firing combustion burner, includes a burner casing configured to receive a fuel-air mixture at a burner inlet and to provide hot combustion gas at a burner output, a combustion substrate disposed within the burner casing, the substrate having a shape comprising at least a semi-cone or a flat surface or equivalent shape, having a substrate porosity defined by a plurality of pores, and having a substrate inner surface and a substrate outer surface, the substrate configured to receive the fuel-air mixture at the outer surface of the substrate, the fuel-air mixture passing through the pores at a mixture flow rate from the substrate outer surface toward the substrate inner surface, and the burner configured such that, in operation, the fuel-air mixture ignites near the plurality of pores to form a respective plurality of flamelets, each flamelet corresponding to one of the pores.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/001,230, filed on Aug. 24, 2020, which is a continuation-in-part ofU.S. patent application Ser. No. 16/285,119, filed on Feb. 25, 2019,which claims priority to U.S. Provisional Patent Application Ser. No.62/634,476, filed on Feb. 23, 2018 and U.S. Provisional PatentApplication Ser. No. 62/634,520, filed on Feb. 23, 2018, and whichclaims priority to PCT Patent Application Serial No. PCT/US2019/019441,filed on Feb. 25, 2019, which claims priority to U.S. Provisional PatentApplication Ser. No. 62/634,520, filed on Feb. 23, 2018, the contents ofeach application cited above are incorporated herein by reference intheir entirety to the extent permissible by applicable law.

BACKGROUND (1) Field

This application relates to a compact premix fuel combustion system forthe purpose of heat generation, methods of using a premix fuelcombustion system, and methods of fluid heating incorporating a compactpremix fuel combustion system.

(2) Description of the Related Art

Premix fuel combustion systems are used to provide a heated thermaltransfer fluid for a variety of commercial, industrial, and domesticapplications such as hydronic, steam, and thermal fluid boilers, forexample. Because of the desire for improved energy efficiency,compactness, reliability, and cost reduction, there remains a need forimproved premix fuel combustion systems, as well as improved methods ofmanufacture thereof.

Incomplete combustion, suboptimal combustion product flow fields, andlarge temperature gradients can result in a decrease in overall burnersystem performance. This is particularly true of combustion systemsincorporated into fluid heating systems for the production of hot water,steam, and thermal fluid for hot liquid or steam for ambient temperatureregulation, hot water consumption, or commercial and industrialapplications. Moreover, residential, commercial, industrial andgovernment uses of combustion systems for a variety of applicationsbenefit from improvements that decrease the size, volume and footprintof these apparatuses, particularly those that utilize premix fuel andair (oxygen) combinations. Thus, there remains a need for an improvedcompact premix fuel combustion system having improved thermalefficiency.

SUMMARY

Disclosed herein is an inward firing premix burner combustion system.

Also disclosed is an inward firing premix burner combustion system witha composite semi-cone combustion substrate.

Also disclosed is an inward firing premix burner combustion system witha composite semi-cone combustion substrate and a guide or baffle fordirecting the fuel-air mixture.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the figures, which are exemplary embodiments, and whereinthe like elements are numbered alike.

FIG. 1A shows an illustration of the elements used to define semi-conegeometry, in accordance with embodiments of the present disclosure.

FIG. 1B shows a perspective diagram of a truncated cone in accordancewith embodiments of the present disclosure.

FIG. 1C shows a perspective diagram of a semi-cone in accordance withembodiments of the present disclosure.

FIG. 1D shows a perspective diagram of a composite semi-cone inaccordance with embodiments of the present disclosure.

FIG. 1E shows a perspective diagram of a composite semi-cone withoutcylindrical sections in accordance with embodiments of the presentdisclosure.

FIG. 2 shows a cross-sectional diagram of an embodiment of a jet burnercombustion system in the vertical orientation.

FIG. 3 shows a cross-sectional diagram of an embodiment of a premixburner in the vertical orientation.

FIG. 4 shows a cross-section of calculated streamlines for a simulatedflow in an embodiment of an outward-firing burner combustion system inthe vertical orientation in accordance with embodiments of the presentdisclosure.

FIG. 5 shows a cutaway diagram of an embodiment of a premix combustionsystem with a single semi-conical combustion substrate in accordancewith embodiments of the present disclosure.

FIG. 6A shows an illustration of the velocity vectors comprising thecalculation of the combustion flame equilibrium ratio (p) in the regionbetween a porous combustion substrate and a flamelet in accordance withembodiments of the present disclosure.

FIG. 6B shows an illustration of the velocity vectors comprising thecalculation of the combustion flame equilibrium ratio (p) in the regionbetween a porous combustion substrate and a flame front in accordancewith embodiments of the present disclosure.

FIG. 6C shows an illustration of the symmetric pores arranged in aregular distribution in a section of a porous combustion substrate inaccordance with embodiments of the present disclosure.

FIG. 6D shows an illustration of the circular pores arranged distributedin a section of a porous combustion substrate in accordance withembodiments of the present disclosure.

FIG. 6E shows an illustration of non-circular pores arranged in aregular distribution in a section of a porous combustion substrate inaccordance with embodiments of the present disclosure.

FIG. 6F shows an illustration of an embodiment of a three-dimensionalstructure for a pore of a porous combustion substrate in accordance withembodiments of the present disclosure.

FIG. 6G shows an illustration of circular holes and slots arranged in aregular distribution in a section of a porous combustion substrate inaccordance with embodiments of the present disclosure.

FIG. 6H shows a perspective drawing of the premix fuel-air flow field inthe burner through the pores of a semi-cone substrate with an acutesubstrate angle in accordance with embodiments of the presentdisclosure.

FIG. 6I shows a perspective drawing of the premix fuel-air flow field inthe burner through the pores of a semi-cone substrate with an acutesubstrate angle and proximal diameter equal to zero in accordance withembodiments of the present disclosure.

FIG. 6J shows a perspective drawing of the premix fuel-air flow field inthe burner through the pores of a semi-cone substrate with an acutesubstrate angle and an instrument conduit between the proximal end ofthe substrate and the burner head in accordance with embodiments of thepresent disclosure.

FIG. 6K shows a perspective drawing of the premix fuel-air flow field inthe burner through the pores of a semi-cone substrate with substrateangle equal to zero and an instrument conduit between the center of thesubstrate and the burner head in accordance with embodiments of thepresent disclosure.

FIG. 6L shows a perspective drawing of the premix fuel-air flow field inthe burner through the pores of a semi-cone substrate with substrateangle equal to zero and an instrument package near the perimeter of thesubstrate in accordance with embodiments of the present disclosure.

FIG. 6M shows a perspective drawing similar to FIG. 6L with instrumentpackage located on a side in accordance with embodiments of the presentdisclosure.

FIG. 7 shows a cross-section diagram of an embodiment of a premixcombustion system with a single semi-conical combustion substrate and aflow baffle in accordance with embodiments of the present disclosure.

FIG. 8 shows a cutaway diagram of an embodiment of a premix combustionsystem with a single semi-conical combustion substrate and a flow bafflein accordance with embodiments of the present disclosure.

FIG. 9 shows a cutaway diagram of an embodiment of a premix fuel flowbaffle for a combustion system with a single semi-conical combustionsubstrate in accordance with embodiments of the present disclosure.

FIG. 10 shows a top view of an embodiment of a premix fuel flow bafflefor a combustion system with a single semi-conical combustion substratein accordance with embodiments of the present disclosure.

FIG. 11 shows a cross-section of calculated streamlines for a simulatedflow of an embodiment of a premix combustion system with a singlesemi-conical combustion substrate and a flow baffle in accordance withembodiments of the present disclosure.

FIG. 12 shows a cross-sectional diagram of calculated velocity vectorsfor a simulated flow of an embodiment of a premix combustion system witha single semi-conical combustion substrate and a flow baffle inaccordance with embodiments of the present disclosure.

FIG. 13 shows a cross-sectional diagram of calculated streamlines for asimulated flow of an embodiment of a premix combustion system with asingle semi-conical combustion substrate and a flow baffle in accordancewith embodiments of the present disclosure.

FIG. 14 shows a cross-sectional diagram of an embodiment of a premixcombustion system with a plurality of semi-conical combustion substratesand a flow baffle in accordance with embodiments of the presentdisclosure.

FIG. 15 shows a prospective view of an embodiment of a premix combustionsystem with combustion substrates of various substrate angles, including90 degrees, juxtaposed to illustrate a sequence of design options withvarying surface areas in accordance with embodiments of the presentdisclosure.

FIG. 16 shows a perspective view of an embodiment of a premix combustionsystem with a combustion substrate at a substrate angle of 90 degrees(flat anulus) in accordance with embodiments of the present disclosure.

FIG. 17 shows a perspective view of an embodiment of a premix combustionsystem with a combustion substrate at a substrate angle of 90 degreesdisplaying the detail of fixing the substrate to the burner head and theregular pattern of pore holes and slots in accordance with embodimentsof the present disclosure.

FIG. 18 shows a perspective view of an embodiment of a premix combustionsystem with a combustion substrate at a substrate angle of 90 degreesdisplaying the detail of the pore structure comprising a hole and slotconfiguration in accordance with embodiments of the present disclosure.

FIG. 19A shows a perspective view of an embodiment of a premixcombustion system with a combustion substrate at a substrate angle of 90degrees (flat anulus) with axial premix flow and a premix flow mixinggrid upstream in accordance with embodiments of the present disclosure.

FIG. 19B shows a side view of an embodiment of a premix combustionsystem with a spherical cap combustion substrate with axial premix flowand a premix flow mixing grid upstream in accordance with embodiments ofthe present disclosure.

FIG. 20 shows a perspective view of a combustion substrate at asubstrate angle of 90 degrees (flat plate) with a hexagonal perimeter inaccordance with embodiments of the present disclosure.

FIG. 21A shows a perspective view of a creased combustion substrate inaccordance with embodiments of the present disclosure.

FIG. 21B shows a cross-sectional view of a creased combustion substratewith a crease angle of ϕ in accordance with embodiments of the presentdisclosure.

FIG. 22A shows a perspective view of a premix combustion substrate at asubstrate angle of 90 degrees (flat plate) with circular substrate poreregions distributed symmetrically in accordance with embodiments of thepresent disclosure.

FIG. 22B shows a cross-sectional view of a premix combustion substrateat a substrate angle of 90 degrees (flat plate) with circular substratepore regions distributed symmetrically in accordance with embodiments ofthe present disclosure.

FIG. 23A shows a perspective view of a premix combustion substratecomprising a hexagonal prism in accordance with embodiments of thepresent disclosure.

FIG. 23B shows a transverse view of a premix combustion substratecomprising a hexagonal prism in accordance with embodiments of thepresent disclosure.

FIG. 24A shows a perspective view of a premix combustion substratecomprising a spherical cap in accordance with embodiments of the presentdisclosure.

FIG. 24B shows a transverse view of a premix combustion substratecomprising a spherical cap in accordance with embodiments of the presentdisclosure.

FIG. 25 shows a perspective drawing of the premix fuel-air flow field inthe burner through the pores of a semi-cone substrate with an acutesubstrate angle, a, and height, H, in accordance with embodiments of thepresent disclosure.

FIG. 26 shows the relationship between surface area and semi-conesubstrate height, H, for an example premix combustion system inaccordance with embodiments of the present disclosure.

FIG. 27 shows a cutaway diagram of an embodiment of a premix combustionsystem with a single semi-conical combustion substrate in accordancewith embodiments of the present disclosure.

FIG. 28 shows cutaway diagram showing an expanded view of an embodimentof the mesh and substrate structure of the combustion diffuser inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

As further discussed herein, the Applicants have discovered that outwardfiring combustion systems can suffer incomplete combustion due to thesmall and constrained combustion volume available, large temperaturegradients that can result in material and performance failures, andundesirable flow characteristics of the hot combustion gases andproducts can be produced in the apparatus.

Disclosed is an improved premix fuel combustion system for applicationsthat require heat generation which provides improved efficiency,apparatus lifecycle and performance by alleviating or eliminating thesedisadvantages.

While not wanting to be bound by theory, the following nomenclature isuseful in the detailed description that follows:

Consistent with convention, a cone is a geometric surface that can beused to describe certain aspects of embodiments of the presentdisclosure, e.g., a combustion surface or substrate (as discussedhereinafter). FIG. 1A illustrates key concepts. A cone 118 is a surfacedefined by a ray called the generator 116 emanating from a fixed pointcalled the vertex 102 which intersects a fixed plane curve called thedirectrix 112. The directrix, as a geometric curve, need not be eithercontinuous or convex but, when it is, it defines an interior to the cone(normal vector oriented toward the volume containing the intersectionwith the axis) and an exterior. The axis 114 of the cone is the straightline passing between the vertex 102 and center 120 of the plane curvedefined by the directrix 112. If the axis 114 is perpendicular to theplane of the directrix 112, it is a right cone; otherwise, it is anoblique cone. If the directrix 112 is a circle, the cone 118 is acircular cone. If the axis 114 is perpendicular to the directrix 112plane for a circular cone, the cone 118 is a right-circular cone. Asemi-cone 100 is a section of a cone surface bounded between byintersecting a cone with at most two 2-dimensional surfaces. In FIG. 1A,the illustrated cone 118 is intersected by a surface 104 proximal to thevertex 102, forming an upper or proximal semi-cone edge 106. The surface104 need not be planar or perpendicular to the axis 114 or any generator116, and the proximal edge 106 need not be a plane curve. Theillustrated cone in FIG. 1A is also intersected by a surface 108 distalfrom the vertex 102, forming a lower or distal edge 110. The surface 108need not be planar or perpendicular to the axis 114 or any generator116, and the distal edge 110 need not be a plane curve. The resultingsemi-cone 100 is the surface of the cone 118 bounded above by theproximal edge 106 and by the distal edge 110 below. In the degeneratecase, the proximal surface 104 intersects the cone 118 only at thevertex 102, wherein the semi-cone 100 is the surface of the cone 118between the vertex 102 and the distal edge 110. FIG. 1C show aperspective diagram of a semi-cone 124 with a non-planar proximal edge126. A semi-cone wherein the cone 118 is intersected by proximal 104 anddistal planar surfaces 108 is a truncated cone. A semi-cone wherein thecone 118 is intersected by parallel proximal 104 and distal planarsurfaces 108 is a frustum. A semi-cone wherein the cone 118 is a rightcircular cone, the proximal 104 and distal surfaces 108 are planar andperpendicular to the axis 114 is a right frustum. FIG. 1B shows aperspective diagram of a right frustum 122. A composite semi-cone is acomposition of one or a plurality of semi-cones and zero, one or aplurality of cylinders disposed along their edges. FIG. 1D shows aperspective diagram of a composite semi-cone 128. FIG. 1E shows aperspective diagram of a composite semi-cone 129 without a cylindricalsection.

For a semi-cone, the generator angle (alpha or a, as discussed furtherherein, e.g., regarding an angle of a combustion surface or substrate asdescribed herein) is the angle 114 formed between a specific generatorray 116 and the axis 114 at the vertex 102. For a right circularsemi-cone, right circular truncated cone or right circular frustum, allthe generator angles are equal and a unique generator angle can bedetermined.

A semi-cone with a generator angle of ninety degrees (90°) is a flatplate, surface, disk or annulus and the limit of a family of semi-conesthat share a common distal end dimensions and shape.

A burner is a combustion system designed to provide thermal energythrough a combustion process to apparatuses used for a variety ofapplications. The burner may include, depending upon the fuel,combustion geometry and target application, a burner head that supportsthe combustion process, one or a plurality of nozzles or orifices, airblower with damper, burner control system, shut-off devices, fuelregulator, fuel filters, fuel pressure switches, air pressure switches,flame detector, ignition devices, air damper and fuel valves andfittings. Typical burner systems range in capacity from 30 kW to 1,500kW (approximately 40 HP to 2,100 HP) and can be adapted to a wide rangeof uses including incinerators, boilers, drying systems, industrialovens and furnaces.

A package burner is a burner combustion system designed to beincorporated as a standalone modular subsystem unit into apparatusesused for a variety of applications. The package burner may include,depending upon the fuel, combustion geometry and target application, anintegrated subsystem comprising a burner head that supports thecombustion process, one or a plurality of nozzles or orifices, airblower with damper, burner control system, shut-off devices, fuelregulator, fuel filters, fuel pressure switches, air pressure switches,flame detector, ignition devices, air damper and fuel valves andfittings. Typical package burner systems range in capacity from 30 kW to1,500 kW (approximately 40 HP to 2,100 HP) and can be adapted to a widerange of uses including incinerators, boilers, drying systems,industrial ovens & furnaces.

In the discussion that follows, we distinguish three types of physicalcombustion mechanisms. First, “volume combustion” occurs where afuel-air mixture is ignited in a spatial volume. A physical structuremay contain the combustion process, such as in a cavity burner, but thedetails of the structure do not directly participate in thethermodynamic combustion process. Second, for “surface combustion”, thecombustion process (or a majority thereof) occurs directly upon—or verynear, or largely in contact with—a burner combustion surface. In somecases, some form of physical insulating or separation layer may beneeded at the burner surface to ensure the burner surface does not gettoo hot or to provide otherwise needed separation from the surface. Thephysical, geometrical and material characteristics of the surfacecontribute to determining the thermodynamic physics. Third, in“suspended flame combustion” (SF combustion), the combustion process (ora majority thereof) occurs near—but not directly on—the surface of acombustion substrate, which provides physical support for the generationof the flame front. In some conditions, a small portion of the flame maycontact the burner surface (as described more hereinafter). In SFcombustion, the flame front (or a majority thereof) is suspended near apositional equilibrium at a distance from the substrate determinedpartly by a balance of opposing forces due to fuel-air mass flow andflame migration toward its fuel source. If the fuel-air mass flow isreduced below a threshold, the flame front can approach the substrateand enter a regime of surface combustion. If the fuel-air mass flow isincreased above a threshold, the flame front can enter a regime ofvolume combustion.

A boiler is a fluid heating system incorporating a heat exchanger thatmay be used to exchange heat between any suitable fluids, e.g., a firstfluid and the second fluid, wherein the first and second fluids may eachindependently be a gas or a liquid. In the disclosed system, the firstfluid, which is directed through the heat exchanger core, is a thermaltransfer fluid, and may be a combustion gas, e.g., a gas produced byfuel fired combustor, and may comprise water, carbon monoxide, nitrogen,oxygen, carbon dioxide, combustion byproducts or combination thereof.The thermal transfer fluid may be a product of combustion from ahydrocarbon fuel such as natural gas, propane, or diesel, for example.

Also, the second fluid, which is directed through the pressure vesseland contacts an entire outer surface of the heat exchanger core, is aproduction fluid and may comprise water, steam, oil, a thermal fluid(e.g., a thermal oil), or combination thereof. The thermal fluid maycomprise water, a C2 to C30 glycol such as ethylene glycol, aunsubstituted or substituted C1 to C30 hydrocarbon such as mineral oilor a halogenated C1 to C30 hydrocarbon wherein the halogenatedhydrocarbon may optionally be further substituted, a molten salt such asa molten salt comprising potassium nitrate, sodium nitrate, lithiumnitrate, or a combination thereof, a silicone, or a combination thereof.Representative halogenated hydrocarbons include1,1,1,2-tetrafluoroethane, pentafluoroethane, difluoroethane,1,3,3,3-tetrafluoropropene, and 2,3,3,3-tetrafluoropropene, e.g.,chlorofluorocarbons (CFCs) such as a halogenated fluorocarbon (HFC), ahalogenated chlorofluorocarbon (HCFC), a perfluorocarbon (PFC), or acombination thereof. The hydrocarbon may be a substituted orunsubstituted aliphatic hydrocarbon, a substituted or unsubstitutedalicyclic hydrocarbon, or a combination thereof. Commercially availableexamples include Therminol® VP-1, (Solutia Inc.), Diphyl® DT (Bayer A.G.), Dowtherm® A (Dow Chemical) and Therm® S300 (Nippon Steel). Thethermal fluid can be formulated from an alkaline organic compound, aninorganic compound, or a combination thereof. Also, the thermal fluidmay be used in a diluted form, for example with a concentration rangingfrom 3 weight percent to 10 weight percent, wherein the concentration isdetermined based on a weight percent of the non-water contents of thethermal transfer fluid in a total content of the thermal transfer fluid.

An embodiment in which the thermal transfer fluid comprisespredominately gaseous products from combustion of natural gas orpropane, and further comprises liquid water, steam, or a combinationthereof and the production fluid comprises liquid water, steam, athermal fluid, or a combination thereof is specifically mentioned.

A jet burner is a type of (non-premix) burner combustion system whereinfuel is ejected from one or a plurality of orifices or nozzles, and thelean or partially oxygenated fuel is ignited to produce a flame.

Disclosed in FIG. 2 is an embodiment of a jet burner combustion system242. Fuel in a primarily vapor state 216 enters an inner annular channel220 through a conduit 218 and flows 244 under pressure through openingsin the burner head 222 into the region 232 of the primary reaction zone234. Air 210 flows through an opening 226 in the top head 228 underpressure provided by a fan (not shown). The air flows 204 in the spacebetween the inner wall of the blast tube 208 and the outer wall of theburner 238 and through orifices in the burner head 222 into the regionsupporting the jet flame 200. In this embodiment, a second vapor fuelstream 212 flows through a conduit 214 into an outer annular channel224. The second fuel stream 206 passes through a series of injectors 207to be aerated by mixing with the air flow 204, providing a leanermixture to feed the secondary reaction zone 202 of the flame 200. Therich fuel stream flows into a manifold 240 that provides an increase inflow velocity as the fuel stream passes through openings in the burnerhead 222. Note that neither the rich primary fuel stream 216 nor thelean aerated secondary fuel stream 212 contain fuel-oxygen mixturescapable of auto-ignition at the temperature and pressure present ininner 220 and outer 224 fuel channels.

The flame 200 produced by the ignited fuel jet stream is a rotatingstructure 236 and can extend in length L_(f) a significant distance inthe furnace 230 cavity. An example of a jet burner combustion system isthe Fulton 40-60 Horsepower LONOX® Burner where the flame may betwo-to-four feet (0.6 to 1.2 meters) in length and occupy over half thelength of the furnace 230.

Moreover, the jet burner embodiment of FIG. 2 exhibits other undesirablecharacteristics. First, the velocity of the fuel vapor streaming throughorifices in the burner head contributes importantly to the separationdistance between the burner head 222 and the flame 200 front. As thevapor velocity decreases, the distances between the flame front andburner head likewise decreases. Extended operation of the burner at alow turndown (ratio between burner maximum power output and low-poweroperating point)—equivalently, small separation distance between theburner head and flame front—can cause material failures of thecomponents, short mean-time-between-failure (MTBF), and reduced burnerlifecycle.

Second, to achieve the higher pressure required at the burner head, boththe air stream 210 and the lean 212 and rich 216 fuel flows must bemaintained at relatively high pressures. That is, a significant fractionof the fan power used to drive these flows must be expended to overcomethe pressure drops from the air 226, lean fuel 214 and rich fuel 218conduits to the burner head 222 and maintain a relative high flowvelocity.

Third, the mixing of the lean fuel 214 and rich fuel 218 flow streamswith the air flow 204 is primarily generated by the flow of the fuelsthrough small orifices in the burner head 222. Low turndown ratiosconsequently imply a reduction in fuel-air mixing, which can increasethe production of incomplete combustion byproducts and undesirableemissions (e.g., NOx). Hence, the requirement for higher air and fuelflow velocities imposes limitations on low power operation, durability,lifecycle, maintenance requirements and emission characteristics.

The long flame length characteristic of a jet burner flame can bemitigated by using a porous substrate to support the flame, breaking thesingle long flame structure into many small flames concentrated in acompact region. FIG. 3 shows a cross-sectional schematic of anembodiment of an outward-firing premix burner 320 contained within afurnace 230A. A premixed combination of predominately vapor fuel and air310 enters the burner inlet 311. In this embodiment the burner has thegeometry of a cylindrical annulus, closed at the end distal from theinlet 314. The outer cylindrical combustion substrate 318 is porous andpermits the flow of the premixed fuel-air combination. The fuel-airmixture is directed 316 outward along the inner face of the burner cap314 to the inner region 312 behind of the porous outer burner combustionsubstrate 318. The premix fuel-air combination passes through the poresin the burner combustion substrate 318 and is ignited to form a densecomposite region of flame 304, the flame front hovering over thecylindrical burner combustion substrate by the mass flow 306 of thefuel-air mixture emanating through each of the substrate pores. Theresulting flame is typically monitored using a sensor 308 that candetect when the flame is extinguished and/or used as an element in acontrol system to, for example, modulate the flow rate and/orconcentrations of the premix fuel-air mixture.

In a shell- and tube boiler heat exchanger application, the hotcombustion products flow into the body of the furnace 230A where theypass through the heat exchanger tubesheet 302 and into the heatexchanger tubes 300. Thermal energy generated by combustion of thepremix fuel-air mixture in the region of the composite flame 304 istransferred across the thin walls of the heat exchanger tubes 300 to theproduction fluid inside the pressure vessel 322 sealed at one end to thefurnace by the top head 228A.

One disadvantage to the outward firing geometry is that the compositeflame region 304 and hot combustion products 306 can impinge upon theinner surface of the furnace 230A, depending upon the fuel-air mass flowthrough the pores, the dimensions of the space between the burnercombustion substrate 318 and the inner furnace wall 203A. Furthermore,the geometry of outward firing burners removes a substantial volume fromthe furnace cavity, reducing the volume available for combustion. As aresult of the reduced volume, incomplete combustion occurs which lowersefficiency and increases the production of incomplete combustionproducts, including environmental contaminates.

Moreover, the flow of hot combustion products is guided by the relativegeometry of the burner combustion substrate 318 and the furnace 230Acavity. FIG. 4 shows streamlines generated by a computational fluiddynamic (CFD) model simulation of the burner geometry shown in FIG. 2,and illustrates some of the flow challenges. The premix fuel-air mixtureflows 400 into the burner inlet 311A, through the burner interior 402sealed by the top head 228B and is directed through the pores in thecylindrical burner combustion substrate 318A. In this outward-firingarrangement, the fuel-air mixture is directed outward through thecombustion where it is ignited 404 in the region of high temperature.The combustion products flow 405 in the restricted space between thecylindrical burner combustion substrate 318A and the inner furnace wall230B. Due to the geometrical cavity constraints, the flow may form avortex 406 where the flow can be stagnant 407. Moreover, the flowstreamlines 408 traversing radially from the edge of the tubesheet 302Atowards the center creates a large temperature gradient across the faceof the tubesheet, so that heat exchanger tube openings 300A at theperimeter of the tubesheet receive flow at a lower average temperaturethan heat exchanger tubes located closer to the center.

In what follows, we define the term “inward-firing” to be aconfiguration wherein the combustion flame structure is oriented alongthe pre-mix flow streamlines substantially towards the interior of thefurnace volume or cavity. Furthermore, the flame structure may besupported by a “convex” substrate wherein the substrate creates a volumeextending outward from the furnace cavity, or “concave” wherein thesubstrate forms a volume extending into the furnace cavity. For example,FIG. 5 shows an inward-firing, convex configuration comprising asemi-cone combustion substrate. The case where the substrate has theshape of a flat plate (e.g., generator angle of 90 degrees in the caseof a right-circular semi-cone) is merely a transition case between thefamily of convex and concave substrate structure geometries.

The inventors have unexpectedly discovered that an inward-firing burnergeometry alleviates many of the disadvantages described above. FIG. 5shows a cutaway diagram of an embodiment of an inward-firing premixburner comprising a semi-cone combustion substrate, although someadvantages of inward-firing premix burner embodiments discovered by theinventors are not limited to the composite semi-cone geometry. Asemi-cone shaped combustion substrate 500 is disposed between the burnertop head 503 and the inner surface of the furnace 230C. In thisembodiment, the burner combustion substrate is a right circular frustumwherein the proximal edge 505 is a planar circle perpendicular to alongitudinal (or axial) axis 509 with proximate diameter D_(p) anddistal edge 507 a planar circle perpendicular to the longitudinal axis509 with distal diameter D_(d), with height H. The burner combustionsubstrate angle α in a right frustum embodiment is then determined tobe:

α=arctan[(D _(d) −D _(p))/H]  Eq. 1

Dimensions of the combustion substrate depend upon the burner power,capacity, performance and size requirements of a specific application.Proximal diameters (D_(p)) between 1 inch and 59 inches is specificallymentioned. Distal diameters (Dd) between 2 inches and 60 inches isspecifically mentioned. Substrate height (H) between 1 inch and 60inches is specifically mentioned.

In some embodiments, the region of the cone circumscribed by theproximal edge 505 may be open (no endcap) or closed by an endcap, alsoshown in FIG. 18 as the surface to which the sensor 308 and the ignitor502 are mounted or disposed on. If closed, the endcap may be perforatedwith pores or covered by a mesh to form an “active” endcap (not shown),or unperforated or solid to form an “inactive” endcap (as shown in FIG.18). In the case of an active (perforated) endcap, the endcap mayparticipate in allowing the passage of premix fuel and supportinginward-firing flame oriented towards the furnace cavity. In that case,there may be holes or ports for the wall 632 (FIG. 18) to allow the fuelto access and pass through the perforated endcap.

The semi-cone sections of the burner combustion substrate angle may haveany suitable generator angle between 1 degree, 2 degrees, 3 degrees, 4degrees, 5 degrees, 10 degrees to 11 degrees, 12 degrees, 13 degrees, 14degrees, 15 degrees, 16 degrees, 17 degrees, 18 degrees, 19 degrees, 20degrees, 21 degrees, 22 degrees, 23 degrees, 24 degrees, 25 degrees, 26degrees, 27 degrees, 28 degrees, 29 degrees, 30 degrees, 31 degrees, 32degrees, 33 degrees, 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38degrees, 39 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80degrees, 85 degrees, and 90 degrees wherein the foregoing upper andlower bounds can be independently combined. For the right circularsemi-cone, right circular truncated cone, and the right circularfrustum, the burner combustion substrate angles between 18 degrees and35 degrees is specifically mentioned. For the right circular semi-cone,right circular truncated cone, and the right circular frustum, theburner combustion substrate angle of 25 degrees is also specificallymentioned.

In some embodiments, a burner combustion substrate angle α may be 90degrees which corresponds to a flat structure, surface, plate, disk orannulus, which may be viewed as a degenerate semi-cone that is the limitof a family of semi-cones with diameter, D_(d). For the right circularsemi-cone, right circular truncated cone, and the right circularfrustum, the burner combustion substrate angle α=90 degrees isspecifically mentioned.

The burner combustion substrate is porous to the flow of premix fuel-airmixtures predominately in a vapor state. Substrate pores 506 aredistributed over the area of the burner combustion substrate to supporta flame front in the burner combustion cavity 635 near the interiorsurface. (The pore 512 size in a local area 510 are exaggerated in thediagram for clarity and are not meant to be to scale.) The combustionprocess may be monitored by a sensor 308A which can detect if the flameis extinguished.

In the embodiment shown a premix(ed) fuel-air mixture 514 enters theinlet 504 of the burner and flows within a burner pre-combustion cavity631 and around and through the burner combustion substrate 500 inwardtoward the longitudinal (or axial) axis 509. The fuel-air mixture ratiois arranged so that the premix fuel is ignited near the interior surfaceto form a flame structure suspended over the interior surface of theburner combustion substrate, within a burner combustion cavity 635.

The flame structure may comprise individual flamelets—relatively small,distinct and stable laminar regions of combustion—which may merge athigher combustion production conditions and may form a flame frontsuspended a predetermined distance the substrate as described below.

In a boiler application comprising a shell and tube heat exchanger, thecombustion products (e.g., hot gases, particulate byproducts) flow 518towards the tubesheet 302B where they pass through the openings 300B ofthe heat exchanger tubes 508. Heat generated by the combustion processis transferred across the walls of the heat exchanger tubes 508 toproduction fluid occupying the space between the outer surfaces of thefurnace 230C and heat exchanger tubes 508 and the inner surface of thepressure vessel 322A, sealed at one end by the boiler top head 228C.

Without being bound by theory, the burner combustion substrate providesa physical structure to support the flame front generated when thepremix fuel-air mixture is ignited, and the porosity of the substratedetermines certain aspects of the resulting combustion process asillustrated in FIG. 6A which shows a region around a single pore 512Abounded by a cross-section view of the porous substrate 601. The premixfuel-air mixture is directed from an outside through the pore spacebounded by the pore 512A perforation walls to an inside of the burnersubstrate above the pore opening called the preheating zone 603. Notethat in normal operation the premix fuel-air mixture is below theautoignition temperature of the fuel premix in the interior of the pore602 and the preheating zone 603. As the premix fuel-air mixture iscarried by the flow momentum with velocity v_(f) ^(normal) 607 towardsthe interior of the burner, the temperature rises until it exceeds theautoignition temperature of the premix fuel-air mixture and it ignitesin the reaction zone 605. During stable combustion the preheating zone603 and the reaction zone share a combustion interface 604 that forms apersistent coherent structure. (Persistent and coherent in the sensethat the preheating zone 603, reaction zone 605 and the combustioninterface—while not fixed structures—are also not transient structures,but persistent, recognizable and stable in a relatively longtime-average sense with orderly components that exhibit stochasticallystable properties.) The premix fuel-air mixture combustion primarilyoccurs in the reaction zone bounded releasing heat, gaseous andparticulate byproducts into the burner.

The tendency for the reaction zone to consume the premix fuel-airmixture creates a force toward the pore that tends to move thecombustion interface 604 near its apex over the pore with a velocityv_(g) ^(normal) 608. Thus, these two opposing forces balance at acondition where the flame equilibrium ratio number:

$\begin{matrix}{{1 < \rho} = {\frac{v_{f}^{normal}}{v_{q}^{normal}}\begin{matrix} < \\ \approx \end{matrix}100}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

where, in a time-average sense and the right inequality means “less thanapproximately”, denoting the fact that the upper bound has beenempirically determined by practical examples and should not be construedto limit or constrain the interpretation of the claims. Otherembodiments may possess practical upper bounds that are higher or lowerwhen designed by those skilled in the art. That is, an important designcharacteristic is to select burner substrate construction, porosity andoperation conditions that ensures the flame reaction zone remainsapproximately stationary relative to the pore opening suspended at adistance from the pore.

For certain combinations of pore geometry, which may be referred toherein as the “suspended flamelet” or “suspended flame” state, premixflow rate and operating conditions, the preheating zone 603, combustioninterface 604 and reaction zone 605 remain attached 609 to edges of thepore 512A, forming a stable, persistent structure called a flameletanchored to the interior surface of the burner substrate 601. Becausethe flamelet's preheating zone 603 contains uncombusted fuel-airmixture, it is relatively cool compares to the reaction zone 605. Thatis, the preheating zone 603 serves to insulate the substrate from thehigh temperature of the reaction zone 605. This is a desirable conditionsince it allows for high burner heat production capacity whilesimultaneously maintaining cooler temperatures at the burner substratesurface that promotes longevity of the substrate and reduces thelikelihood of material failure. The separation of the reaction zone 605from the substrate 601 inner surface that promotes this insulativeeffect can be expressed—in a local sense—as the flamelet separationdistance, d_(SFL), 610 from the inner surface of the substrate 601 overthe pore 512A and the apex of the combustion interface 604. In practice,flamelet separation distances for premixtures of natural gas and air arebetween zero (0) inches (surface combustion) and approximately 1.75inches (suspended flame combustion, SF), although the distance will vary(stochastically and as an average distance observed over relatively longtime periods) in practice. In some embodiments, the flamelets mayoverlap depending on the distance between pores, flow rate, and otherconditions.

Under certain operating conditions, which may be referred to herein asthe “suspended flame front” state, particularly when the premix fuel-airmixture flow velocity is high, the flamelets may detach from the innersurface of the burner substrate, as illustrated in the embodiment shownin FIG. 6B. Under such conditions, the flamelets may coalesce into a newcoherent combustion characterized by a flame front 611 suspended over acollection of pores 512B. The flame front formed by separating a layerof uncombusted premix fuel-air mixture 603A flowing through the interiorpore space 602A of the pore 512B into a preheating zone beneath acoalesced reaction zone 612 undergoing primarily volume combustiontypical of a cavity burner. Under narrow operating conditions, thiscoherent structure may maintain a relatively fixed position suspendedover a collection of pores, separated by a suspended flame frontdistance, d_(SFF), 610A from the inner surface of the burner substrate601A when a balance of forces exists between the premix fuel-air mixturewith velocity v_(f) ^(normal) 607A and the opposing force of the flamefront's 611 motion towards the inner surface of the burner substrate601A with opposing velocity v_(g) ^(normal) 613. Note that because theflame front is typically not anchored to the surface of the substrate,the velocity of the flame front may have a non-normal component 614which may tend to shift the position of the reaction zone in time andspace. The suspended flame front state is typically a transient orunstable state, and thus is not typically operated in for sustainedoperation.

The conditions or states described herein with FIGS. 6A and 6B may bereferred to collectively herein as the “suspended flame combustion” orSF combustion, as described hereinbefore.

These principles have been verified using an experimental testapparatus. Based on experimental data, Table 1 shows typical geometryand operating conditions that will exhibit suspended flame (SF)combustion in a burner using a semi-cone substrate geometry.

TABLE 1 Parameter Description and Values Plate Material 439 StainlessSteel Plate Thickness 20 GA, 0.9525 mm Pore Type & Dimensions Slots 1 mm× 6 mm dimensions. Pore Area = 5.79 mm² Number of Slots 1,834 Flow MeanVelocity 1.2 m/s to 27 m/s tested Flow Port Loading 3.69 W/mm² to 82.93W/mm² Burner Input 879765.4 W Cone Area 84,424.2 mm² D_(p) 354 mm D_(d)472 mm Height 25.4 mm

Porosity of the burner combustion substrate can be achieved by a numberof constructive means, so long as they equivalently achieve and maintainthe semi-conical shape and porosity characteristics required by aspecific set of design parameters. Perforations in a solid substrate,including perforations in a metal sheet, are specifically mentioned.

The pore 2-dimensional and 3-dimensional structure, together with thedistribution of pores in the burner combustion substrate, are designedin concert to achieve an operational flame structure required to meetthe specifications a particular application. FIG. 6C shows a uniformdistribution of circular perforations 616 in a local region 510C of asolid continuous burner combustion substrate. The pores 618 may benon-circular, as shown in FIG. 6D, and non-uniformly distributed on theburner combustion substrate. The porosity may result from perforationsin a continuous surface; other equivalent embodiments are possible andknown to those skilled in the art. FIG. 6E shows a local region 510E ofporous substrate wherein the pore 620 shape is unsymmetrical. Finally,some or all of the burner combustion substrate pores 624 may have a3-dimensional structure in a region 622 of the substrate designed topromote certain flow or flame characteristics. A pore with the 3-D shapeof a nozzle is specifically mentioned.

The shapes and distributions of pores can be mixed to produce desirableheat production, pressure drop across the cross-section of the substrateand combustion stability properties as illustrated by the embodimentshown in FIG. 6G. For a region 510F of the burner substrate porosity isgenerated by a regular pattern of slots 626 and holes 628 perforated inthe substrate surface. Without being bound by theory, distributions ofnarrow slots 626 and holes 628 with small diameter tend to promotecombustion stability, but increase the pressure drop acrosscross-section of the burner substrate by presenting a high resistance tothe premix fuel-air flow. Wider slots 626 and holes 628 with largediameters decrease the pressure drop due to flow resistance, but mayincrease the tendency of flame blow-out, flashback and resonanceinstabilities. Empirically, the inventors have found that circular holediameters between 0.5 millimeters and 2 millimeters and slots with widthdimensions between 0.5 millimeters and 2 millimeters and lengthdimensions between 2 millimeters and 15 millimeters provide a practicalbalance of flow and stability characteristics. A circular hole diameterof 1 millimeter is specifically mentioned. A slot with width 1millimeter and length of 6 millimeter is specifically mentioned. Aregular pattern of holes, slots, or holes and slots promotesmanufacturability, but the present disclosure is meant to encompass allregular and irregular patterns of holes or slots or holes and slots incombination with approximately equivalent premix fuel-air flow andcombustion properties. The substrate temperature and pressure drop isalso affected by the fraction of the burner substrate surface that isperforated to produce pores. Empirical results show that a perforatedsurface area of between approximately 5 percent, 6 percent, 7 percent, 8percent, 9 percent or 10 percent of the total substrate surface area toapproximately 20 percent, 22 percent, 24 percent, 26 percent, 28percent, 30 percent, 32 percent, 34 percent, or 36 percent of the totalsubstrate surface area provides practical control of the substratesurface temperature wherein the foregoing upper and lower bounds can beindependently combined. The range 8 percent to 20 percent of the totalsubstrate surface area is specifically mentioned

There are several important advantages to the arrangements in thedisclosed embodiments. A first feature is that—depending upon thespecific parametric choices for design parameters (including pore sizeand density, the fuel-air flow velocity and combustion substrategeometry)—while the burner can be operated in a range of combustionmodes from surface combustion to volume combustion, the geometry issuitable for stable suspended flame (SF) combustion applications. Thisis desirable since the resulting separation distance between the flamefront and the combustion substrate in SFF combustion: (a) relaxes thematerial demands on the substrate in the presence of high temperaturesduring operation, eliminating the need for insulation of the substrate;and, (b) reduces the risk of substrate material failure or contaminationof the pores by combustion byproducts.

A second feature is that the semi-cone combustion substrate geometrypromotes substantial uniformity of the combustion process over theentire interior surface of the substrate. FIG. 6H presents a perspectivedrawing showing a burner combustion system 616 comprising a semi-coneshaped combustion substrate 614. A premix fuel-air mixture 620 entersthe burner casing 520 through the inlet conduit 618 and is distributedby the flow geometry in the annular region formed between the burnercasing and the substrate. The mass flow of fuel-air mixture in acircumferential section 633 of the semi-cone combustion substrate isdetermined by the flow rate 624 through the distribution of pores 622and the surface area of the substrate at that altitude of the semi-cone.At the proximal end 628 of the combustion substrate (proximal to thegeometrical apex), P, the fuel-air flow rate is relatively high and thecircumferential section surface area is low. Conversely, at the distalend 626 of the combustion substrate, D, the fuel-air flow rate isrelatively low and the circumferential section surface area is high. Thevolume of the burner casing 616, the proximal (D_(p)) and distal (D_(d))diameters of the semi-cone combustion substrate and the semi-cone angle,a, as measured from the axis 630 can be selected so that the fuel-airmass flow is substantially uniform along the entire length of thesubstrate. Balancing the local fuel-air mass flow to achieve asubstantially uniform distribution of fuel-air mass flow into the flamefront (and, therefore, heat generation, temperature, flow velocity,etc.) is a feature that distinguishes the embodiments comprising asemi-cone combustion substrate from other alternatives.

Moreover, the burner combustion substrate defines a combustion volumedelineated by the interior surface of the substrate that is optimizedfor improved and complete combustion of the premix fuel-air mixture,homogeneous distribution of the flame front on the interior surface ofthe porous substrate (equivalently, diffuser), and substantialuniformity of the resulting flow field of combustion products.

The desirable flow field and temperature distribution properties persistfor a range of semi-cone burner substrate geometries. FIG. 6Iillustrates an embodiment that shows a perspective drawing of a burner616A comprising a semi-cone shaped combustion substrate 614A with anacute, non-zero substrate angle and proximal diameter equal to zero. Apremix fuel-air mixture 620A enters the burner casing through the inletconduit 618A and is distributed by the flow geometry to the annularburner pre-combustion cavity 631 formed between the burner casing andthe substrate. The mass flow of fuel-air mixture in a circumferentialsection of the semi-cone combustion substrate is determined by the flowrate through the distribution of pores 622A and the surface area of thesubstrate at that altitude of the semi-cone. The premix fuel-air flowsthrough the pores of a semi-cone substrate which ignites within theburner combustion cavity 635, as described herein. Also shown are theigniter 508 and the detector sensor 308A disposed on the substrate in alocation away from the axis centerline.

FIG. 6J illustrates an embodiment that shows a perspective drawing of aburner 616B comprising a semi-cone shaped combustion substrate 614B withan acute, non-zero substrate angle. A premix fuel-air mixture 620Benters the burner casing through the inlet conduit 618B and isdistributed by the flow geometry to the annular burner pre-combustioncavity 631 formed between the burner casing and the substrate. The massflow of fuel-air mixture in a circumferential section of the semi-conecombustion substrate is determined by the flow rate through thedistribution of pores 622B and the surface area of the substrate at thataltitude of the semi-cone. The premix fuel-air flows through the poresof the semi-cone substrate which ignites within the burner combustioncavity 635, as described herein. Also shown are the igniter 508 and thedetector sensor 308B disposed on the substrate in a location on the axiscenterline through a conduit 632 to the burner head.

FIG. 6K illustrates an embodiment that shows a perspective drawing of aburner 616C comprising a semi-cone shaped combustion substrate 614C withsubstrate angle equal to zero. A premix fuel-air mixture 620C enters theburner casing through the inlet conduit 618C and is distributed by theflow geometry in the burner pre-combustion cavity 631 formed between theburner casing and the substrate. The mass flow of fuel-air mixture isdetermined by the flow rate through the distribution of pores 622C andthe surface area. Also shown are the igniter 508 and the detector sensor308C disposed on the substrate in a location on the axis centerlinethrough a conduit 632 to the burner head.

FIG. 6L illustrates an embodiment that shows a perspective drawing of aburner 616D comprising a semi-cone shaped combustion substrate 614D withsubstrate angle equal to zero (i.e., flat plate). A premix fuel-airmixture 620D enters the burner casing through the inlet conduit 618D andis distributed by the flow geometry in the region formed between theburner casing and the substrate. The mass flow of fuel-air mixture isdetermined by the flow rate through the distribution of pores 622D andthe surface area, and combustion occurs within the burner combustioncavity 635, as described herein. Also shown are the igniter 508 and thedetector sensor 308D disposed on the substrate in a location away fromthe axis centerline.

FIG. 6M is similar to the embodiment shown in FIG. 6L, except thesensors 302, 508 are mounted on the side, instead of through thesubstrate plate.

A third feature is that, even when the fuel-air mass flow rate isincreased into the volume combustion regime, the semi-cone geometryalters the cavity flame structure so that the power density isincreased, and a smaller flame is require to achieve a prescribed levelof heat generation. Because the fuel-air mass flow is equallydistributed over the surface of the porous combustion substrate, whendriven into a volume combustion regime the entire length of the flame isequally impinged by the premix fuel. Hence, the structure of the body ofthe flame—normally divided into cool and hot regions—is altered toproduce a hotter, more efficient combustion process. As a result, thesame heat generation capacity is achieved by a smaller flame size withhigher power density, and more complete combustion can occur in asmaller burner cavity.

Moreover, these beneficial aspects may be enhanced by guided control ofthe fuel-air flow field as it impinged on the outer surface of thecombustion substrate. Disclosed are embodiments that further comprise abaffle or guide designed to distribute the incoming fuel-air mixture sothat the local mass flow and velocity is close to (or substantially)uniform over the burner combustion substrate. FIG. 7 shows across-sectional diagram of an embodiment of as inward-firing premixburner comprising a semi-cone combustion substrate 500A. The burnercombustion substrate is porous to the flow of premix fuel-air mixturesin a vapor state. Substrate pores 512A are distributed over the area ofthe burner combustion substrate to support a flame front 516A on theinterior surface. (The pore 512A size, in a local area 510A, isexaggerated in the diagram for clarity and are not meant to be toscale.) The combustion process may be monitored by a sensor 308B whichcan detect if the flame is extinguished.

This embodiment further comprises a flow guide or baffle 700, betweenthe walls of the burner casing 706. In this embodiment the baffle is anunperforated, non-porous substrate in the shape of a semi-cone with anon-planar proximal edge 702 and a planar, circular distal edge 704,disposed between the burner head 503A and the inner furnace 230D wall.Most of the premix fuel-air mixture 514A entering the burner inlet 504Aimpinges upon the baffle 708 so that the high-velocity flow doesn'tdisproportionately impinge upon the combustion substrate immediatelyadjacent to the inlet opening. Instead, the premix fuel-air flow isprimarily directed around the outside of the baffle between the baffle700 and the burner casing 706. The baffle proximal edge is shaped tothat the fuel-air flow spills over the baffle proximal edge 702, passes710 through burner combustion substrate pores 512A, and is ignited toform a combustion flame 516A since, by design, the premix fuel-airmixture is in the correct ratio to support ignition at the operatingtemperature and pressure. At the beginning of burner operation,combustion can also be initiated by a spark from an igniter 502A.

In a boiler application comprising a shell and tube heat exchanger, thecombustion products (e.g., hot gases, particulate byproducts) flowtowards the tubesheet 302C where they pass through the openings 300C ofthe heat exchanger tubes. Heat generated by the combustion process istransferred across the walls of the heat exchanger tubes to productionfluid occupying the space between the outer surfaces of the furnace 230Dand heat exchanger tubes and the inner surface of the pressure vessel322B, sealed at one end by the boiler top head 228D.

FIG. 8 shows a cutaway diagram of the inward-firing premix burnercomprising a semi-cone combustion substrate and further comprising asemi-conical baffle disclosed in FIG. 7. The burner combustion substrate700A is porous to the flow of premix fuel-air mixture in a vapor state.Substrate pores 512B are distributed over the area of the burnercombustion substrate 500B to support a flame front on the interiorsurface. (Shown are pores in a small area 510B of the combustionsubstrate, not to scale.) The combustion process may be monitored by asensor 308C which can detect if the flame is extinguished, andcombustion can also be initiated by a spark from an igniter 502B.

A flow baffle 700A guides the fuel-air mixture flow between baffle andthe walls of the burner casing 706A. As before, in this embodiment thebaffle is an unperforated, non-porous substrate in the shape of asemi-cone with a non-planar proximal edge 702A and a planar, circulardistal edge 704A, disposed between the burner head 503B and the innerfurnace 230E wall. Most of the premix fuel-air mixture 514B entering theburner inlet 504B impinges 708A upon the baffle so that thehigh-velocity flow doesn't disproportionately impinge upon thecombustion substrate immediately adjacent to the inlet opening. Instead,the premix fuel-air flow is primarily directed around the outside of thebaffle between the baffle 700A and the burner casing 706A. The baffleproximal edge is shaped to that the fuel-air flow spills over the baffleproximal edge 702A, and passes 710A through burner combustion substratepores 512B.

In a boiler application comprising a shell and tube heat exchanger, thecombustion products (e.g., hot gases, particulate byproducts) flowtowards the tubesheet 302D where they pass through the openings 300D ofthe heat exchanger tubes 508A. Heat generated by the combustion processis transferred across the walls of the heat exchanger tubes toproduction fluid occupying the space between the outer surfaces of thefurnace 230E and heat exchanger tubes 508A and the inner surface of thepressure vessel 322C, sealed at one end by the boiler top head 228E.

FIG. 9 shows details of an embodiment of the baffle used to distributethe premix fuel-air flow field impinging on the outer burner combustionsubstrate shown in FIG. 8. As described above, in this embodiment thebaffle is in the shape of a semi-cone with a non-planar proximal edge702B and a planar, circular distal edge 704B. The fuel-air mixtureentering the burner inlet 504C at the maximum velocity is deflected bythe baffle, directed to stream both behind 904 and in front 900 of thebaffle 704B. Low regions in the proximal edge 702B allow the fuel-airmixture to flow inside the baffle both behind 906 and in the front 902of the baffle. The distal edge 704B of the baffle is disposed on thefurnace wall, and the flow around the distal edge is insignificant tothe flow dynamics in this embodiment.

FIG. 10 shows the fuel-air mixture flow from a cross-sectional viewlooking down on the burner. The flow enters the burner inlet 504D and,separated by the baffle, flows both right 906A and left 902A in thespace between the baffle 700C and the furnace wall 230F. Note that inthis embodiment the axis of the baffle semi-cone is offset from the axisof the burner combustion substrate semi-cone so that the distancebetween the baffle and the furnace wall opposite the burner inlet,h_(o), is smaller than the distance between the baffle and the furnacewall adjacent to the burner inlet, h_(i), with h_(o)<h_(i).

FIG. 11 shows a cross-sectional diagram of the streamlines of acomputation fluid dynamic (CFD) computer model simulation of anembodiment of an inward-firing premix burner comprising a semi-conecombustion system as an element of a fluid heating system (hydronicboiler) as described in FIG. 7. (Simulated burner output: 3 MMBUT/hr(879 kW); natural gas fuel; 16% excess air; water temperature of 180°F.) Each streamline shows the computed path of a unit of mass flowthrough the apparatus. A fuel-air mixture 1100 enters the burner inlet504E and is guided around the burner perimeter by the baffle 700D. Theshape of the baffle's proximal edge 702C permits the flow 1102 of thefuel-air mixture into the region between the baffle 700D and the porousburner combustion substrate 500C where it is ignited. The resulting hotgases and combustion product flow in the interior of the semi-coneburner combustion substrate 1104 and furnace walls 203F in streamlinesthat become nearly parallel 1106 and impinge upon the heat exchangertubesheet 302E.

FIG. 12 shows a cross-sectional diagram of local velocity vectors of acomputation fluid dynamic (CFD) computer model simulation of anembodiment of an inward-firing premix burner comprising a semi-conecombustion system as an element of a fluid heating system (boiler) asdescribed in FIG. 7 and FIG. 11. Each velocity vector shows the computedlocal velocity of a unit of mass flow at a specific location in theapparatus. In this simulation, the fuel-air mixture 1200 enters theburner inlet 504F at a velocity of 40 m/s and is guided around theburner perimeter by the baffle 700E. The shape of the baffle's proximaledge 702D permits the flow 1202 of the fuel-air mixture into the regionbetween the baffle 700E and the porous burner combustion substrate 500Dat a more uniform velocity of 16 m/s where it is ignited. The resultinghot gases and combustion product flow at a nearly (or substantially)uniform velocity of 5 m/s in the interior of the semi-cone burnercombustion substrate 1204 and furnace walls 203G in velocity vectorsthat become nearly parallel 1206 and impinges upon the heat exchangertubesheet 302F.

FIG. 13 shows a perspective diagram of the streamlines of a computationfluid dynamic (CFD) computer model simulation of an embodiment of aninward-firing premix burner comprising a semi-cone combustion system asan element of a fluid heating system (boiler) as described in FIG. 7 andFIG. 11. Each streamline shows the computed path of a unit of mass flowthrough the apparatus. A fuel-air mixture 1300 enters the burner inlet504G and is guided around the burner perimeter by the baffle 700F. Theshape of the baffle's proximal edge 702D permits the flow 1302 of thefuel-air mixture into the region between the baffle 700F and the porousburner combustion substrate 500E where it is ignited. The resulting hotgases and combustion product flow in the interior of the semi-coneburner combustion substrate 1304 and furnace walls 203H in streamlinesthat become nearly parallel 1306 and impinge upon the heat exchangertubesheet 302G.

Thus, a fourth aspect is that the semi-cone combustion substrategeometry promotes substantial homogeneity and substantial uniformity ofthe flow field exiting the burner casing. This is particularly importantin apparatus comprising heat-generating burners for fluid heatingapplications utilizing, for example, shell-and-tube heat exchangers.Referring to FIG. 5, in these applications, non-uniform flow patternsand temperature gradients implies that heat exchanger tubes 508 mayreceive combustion products at different conditions across the tubesheet302B. For example, in the outward firing cylindrical burner of FIG. 4and FIG. 5, flow of combustion gases into the heat exchanger openings300A tends to be cool near the periphery of the tubesheet 302A where theflow has been exposed to the walls of the burner casing 230B and hotnear the center where vortices 407 may develop. Embodiments comprisingsemi-cone combustion substrates can produce substantially uniform flowinto the tubesheet and reduce or eliminate the temperature gradientspresent in alternative embodiments.

Towards this end, in certain embodiments a composite semi-conecombustion substrate is used when optimization of the combustion flowfield over the height, H, requires a change in the local generator angle(alternatively, range of generator angles in the case of a generalsemi-cone). Otherwise, when optimization of the combustion flow fieldcan be achieved using a single semi-cone, a semi-cone, truncated cone orfrustum shape may be used.

A fifth feature is that substantially uniform combustion over thesurface of the substrate and uniformity of the flow field exiting theburner contributes to an increase in thermodynamic efficiency of thecombustion system. A result of the substantially uniform flow field andtemperature distribution of combustion products generated by the premixburner comprising a composite semi-cone combustion substrate is anincrease in overall system thermodynamic efficiency. This is aparticularly important result for applications like fluid heating whereenergy efficiency and reduction of environmentally hazardous byproductsare key.

The inventors have also unexpectedly discovered that a plurality ofconcentric porous combustion porous surfaces or substrates, which may becollectively referred to herein as the “substrate”, can have abeneficial effect on the substantial uniformity of the fuel-air mixturevelocity as it enters the interior of the burner combustion volume. Anynumber of layers or porous structures may be used if desired to make upthe substrate provided they provide the porosity to provide theperformance and function described herein.

FIG. 14 shows a perspective diagram of an embodiment of an inward-firingpremix burner comprising two concentric semi-cone combustion substrates.A first semi-cone shaped combustion substrate 1400 is disposed betweenthe burner top head 503C and the inner substrate of the furnace 230H. Inthis embodiment, a second semi-cone shaped combustion substrate 1402 isdisposed between the burner top head 503C and the inner substrate of thefurnace 230H and concentric to the first semi-cone shaped combustionsubstrate 1400, separated by a distance h.

Both the first 1400 and second 1402 burner combustion substrates areporous to the flow of premix fuel-air mixtures predominately in a vaporstate. Pores 1404 are distributed over the area of the burner combustionsubstrate to support a flame front on the interior surface of the firstburner combustion substrate. (The pore 512C size in a local area 510Fare exaggerated in the diagram for clarity and are not meant to be toscale.) The combustion process may be monitored by a sensor 308D whichcan detect if the flame is extinguished. At startup, combustion may beinitiated using an igniter 502C disposed in the interior of the firstburner combustion substrate.

In the embodiment shown a premix fuel-air mixture enters the inlet 504Hof the burner and flows around and through the burner combustionsubstrate inward to the interior of the burner combustion substrate.

In a boiler application comprising a shell and tube heat exchanger, thecombustion products (e.g., hot gases, particulate byproducts) flowtowards the tubesheet 302E where they pass through the openings 300EB ofthe heat exchanger tubes 508B. Heat generated by the combustion processis transferred across the walls of the heat exchanger tubes 508B toproduction fluid occupying the space between the outer surfaces of thefurnace 230H and heat exchanger tubes 508B and the inner surface of thepressure vessel 322D, sealed at one end by the boiler top head 228F.

The various components of the premix fuel burner combustion system caneach independently comprise any suitable material. Use of a metal isspecifically mentioned. Representative metals include iron, aluminum,magnesium, titanium, nickel, cobalt, zinc, silver, copper, and an alloycomprising at least one of the foregoing. Representative metals includecarbon steel, mild steel, cast iron, wrought iron, a stainless steelsuch as a 300 series stainless steel or a 400 series stainless steel,e.g., 304, 316, or 439 stainless steel, Monel, Inconel, bronze, andbrass. Specifically mentioned is an embodiment in which the premix fuelburner combustion system components each comprise steel, specificallystainless steel. The premix burner combustion system may comprise aburner head, a combustion substrate, a baffle, a furnace wall that caneach independently comprise any suitable material. Use of a steel, suchas mild steel or stainless steel this mentioned. While not wanting to bebound by theory, it is understood that use of stainless steel in thedynamic components can help to keep the components below theirrespective fatigue limits, potentially eliminating fatigue failure as afailure mechanism, and promote efficient heat exchange.

A sixth feature is that of a flat substrate (annular substrate withD_(d) and D_(p) prescribed) is the geometrical limit of a sequence ofsemi-cone combustion substrate configurations within the inventivespecies sharing a common furnace diameter. FIG. 15 shows the furnacewall 2301 bounding a family enclosed by the burner head 228G bounding asequence of semi-cone burner combustion substrates of decreasing angleincluding a substrate with a small (generator) angle 500F, intermediateangle 500G, large angle 500H and an angle of ninety degrees)(90° 500I(flat plate or annulus). (Note that only one burner combustion substratestructure is present in any specific operating configuration embodiment,notwithstanding the multi-layer substrate configuration described aboveand an embodiment of which is illustrated in FIG. 14. FIG. 15 is meantonly to illustrate the relationship of a collection of possiblesubstrates of different angles within the species of semi-cone substrateburners juxtaposed in a prescribed furnace geometry.)

FIG. 15 also shows the burner pre-combustion cavity 631 and instrumentplate located in the center of the substrate disk. A cylinder 532 mayconnect the upper surface 503D to the instrument plate to shield theinstruments from the fuel-air mixture and/or provide external access tothe instruments 502, 308. The walls of the cylinder 632 may be angledshown as dash lines 632A, 632B, 632C in a shape of a cone or othershape, which may help direct the fuel-air mixture toward the flatsubstrate. A similar cylinder is shown in FIG. 16.

A family of semi-cone substrates sharing a common finance diameter(e.g., D_(d) in FIG. 5 and FIG. 6B) possesses the important propertythat the surface area of the substrate supporting the pores increaseswith decreasing substrate angle, a (equivalently, with increasingsemi-cone height). This enables those skilled in the art of burnerdesign to select the combustion substrate geometry to achieve a heatproduction capacity (equivalently, burner surface load, the amount ofheat produced by combustion per unit surface area of substrate surfacein Watts per centimeter squared). That is, for a prescribed furnaceconfiguration with distal diameter (D_(d)) and proximal diameter (DO,the surface area of the substrate is minimum for a substrate angle,α=90°, and increases with decreasing substrate angle. If the designtarget burner load can be achieved using a desired perforation patternand density on a flat (or annular) substrate (α=90°) at a prescribetemperature, this option provides configuration that is easily andcheaply manufactured and still retains desirable premix flow, heatdistribution, temperature and flame combustion characteristics. If theburner load cannot be achieved using this minimal surface area, asemi-cone substrate with angle 0<α<90° is used, which increases theavailable surface area and, thereby, total burner system heat productioncapacity.

FIG. 16 shows an embodiment of the burner combustion systemincorporating a substrate with a substrate angle equal to 90 degreesdisposed in a circular furnace wall of diameter D_(d). Not shown is themounting for mounting plate for the optical sensor and igniter which isdisposed in the opening near the center of the substrate with diameterD_(p). In this embodiment, the furnace geometry is prescribed by thecircular furnace wall 203J that (including the flange mount) defined adistal diameter, D_(d), for the substrate. The substrate 500J issandwiched in the burner to head 228H mounting flange to hold thesubstrate in place for operation. A gas-air premixture 1600 flows intothe inlet conduit 5041 and is dispersed in the volume defined by thesubstrate 500J and the burner head 503D. The gas-air premixturepenetrates 1602 the substrate pores into the combustion volume 1604.

The principles and characteristics of an embodiment similar to thatshown in FIG. 16 was tested using a 1/18th scaled-down instrumentedprototype. The scaled-up results are displayed in Table 2. Theinstruments, e.g., temperature, pressure, flames, gas analyzers, etc.were located on a side of the substrate or burner (not on the substrateflat surface as shown in FIG. 16), also, the fuel-air mixture wasprovided substantially vertically from an inlet at the top of the burner(not from the side as shown in FIG. 16).

TABLE 2 Parameter Description and Values Plate Material 439 StainlessSteel Plate Thickness 20 GA, 0.9525 mm Port Type & Dimensions Slots 1 mm× 4 mm dimensions. Port Area = 3.79 mm² Number of Slots 3,149 Flow MeanVelocity 1.2 m/s to 23 m/s tested Flow Port Loading 3.69 W/mm² to 73.71W/mm² Burner Input 879765.4 W Cone Area (flat plate) 94,469.1 mm² D_(p)0 mm D_(d) 347 mm Height 0 mm

The embodiment test results demonstrate the burner with a combustionsubstrate angle of ninety degrees (flat substrate) and a regular patternof slots exhibits stable suspended flame combustion over a wide range ofpremix fuel-air mixture flow rates, substrate surface loading and heatproduction conditions.

There are equivalent methods for disposing the burner combustionsubstrate on the furnace structure. FIG. 17 shows one simple embodimentof an attachment method that secures the combustion substrate 500K, hereshown as a flat (annular substrate with angle equal to 90 degrees) tothe burner top head 228I; however, this disclosure is not limited tothis specific embodiment but encompasses all equivalent methods ofsecuring the substrate in position for conducting premix flow andsupporting the flame structure near the surface of the substrate. In theembodiment shown the burner combustion substrate 500K extends 1706 intothe space between the burner top head flange 228H and the upper wall ofthe furnace top head 1704. The volume that contains the premix flowbefore it penetrates the pores is defined in part by the wall of theburner head 1708 which is secured to the furnace top head; for instance,using a threaded bolt shaft and nut fastener (not shown), although thisembodiment is only one of several equivalent methods for securing theburner top head to the furnace top head. The burner substrate 500K isperforated to allow flow penetration by the premix fuel-air mixture. Theperforations shown in the embodiment comprise a regular pattern of slots1700 and circular holes, although other perforation patterns may beselected by those skilled in the art of burner design.

The design of the perforation pattern, dimensions and distributions areseparate inventive concepts from the semi-cone substrate structure, andthe resulting flow and temperature properties can be exploited invarious distinct configurations. For example, FIG. 18 shows anembodiment of a semi-cone burner substrate 500L with top head 503Edisposed on the furnace head 228J comprising a pattern of slots 1700Band circular holes 1702B for a substrate with an acute generator angle.The desirable flow, temperature and combustion properties such a porepattern can be expected to have similarities in two different semi-conegeometries, but will also have distinct properties that may be exploitedby one skilled in the art of burner design.

FIG. 19A shows an embodiment of the burner combustion systemincorporating a substrate 500M with a substrate angle equal to 90degrees disposed in a circular furnace wall of diameter D_(d). In thisembodiment, the furnace geometry is prescribed by the circular furnacewall 203K that (including the flange mount) defines a distal diameter,D_(d), for the substrate. The substrate 500M comprises a flange thatextends between the head of the furnace 1801 and the burner head 503Fthat includes a mounting flange 228K, and the assembly is secured usingfasteners 1803 or equivalent. A gas-air premixture 1802 flows axiallyinto the inlet conduit 1805 and is dispersed in the volume defined bythe substrate 500M and the burner head 503F. This embodiment includes apremix flow mixing grid 1800 upstream of the combustion substrate 500M,which may comprise one or more of a course grid of metal fibers,perforated plate of heat resistant material, porous heat-resistancematerial, or the like, that induces turbulence in the flow to promotemixing prior to the flow passing through the pores in the combustionsubstrate 500M that is sufficiently porous to provide flow mixingwithout incurring a large pressure drop in the flow across thestructure. The premix flow mixing grid 1800 has a permeability(percentage of uncovered surface area) between about 20%, 25%, 30%, 35%,40%, or 45% and about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%wherein the foregoing upper and lower bounds can be independentlycombined. The permeability range between about 40% and about 70% isspecifically mentioned. A premix flow mixing grid with a permeability ofabout 60% is also specifically mentioned. The pore structure shown inthis embodiment comprises a combination of circular 1702B and elongated1700B pores, but any of the pore geometries described herein or theirequivalents may be used and are considered within the scope of theclaims. The gas-air premixture penetrates the combustion substrate 500Mthrough the pores 1700B and 1702B into the combustion volume 635circumscribed by the furnace fall 203K, the combustion substrate 500Mand the furnace head 1801. In the described embodiment, the flame rod502 (or, equivalently, optical sensor) and igniter 308 penetratetransversely through the furnace wall 230K, although any of thearrangements described herein or their equivalents may be used and areconsidered within the scope of the claims.

Table 3 display test data collected on a prototype burner correspondingto the configuration shown in FIG. 19A.

TABLE 3 Parameter Units Data D_(d) milimeters 172 Premix DischargePressure w.c. 9.8 Furnace Inlet Pressure w.c. 8.3 Burner Pressure Dropw.c. 1.5 O₂ 4.90% CO₂   9% CO ppm 67 NOx (calculated at 3% O₂) ppm 19.9

Note that the pressure drop (difference between the fan outlet pressureand the furnace inlet pressure) across the burner is only 1.5 inches,which is more than 40% improvement over conventional burner technology.Also, the measured nitrous oxide (NOx) level is below 20 ppm at lowoxygen feed rates (19.9 ppm NOx at 4.90%), and the permeability is about60%.

FIG. 19B shows an embodiment of the burner combustion systemincorporating a combustion substrate in the shape of a concave sphericalcap 500N of height, H, disposed in a circular furnace wall of diameterD_(d). In this embodiment, the furnace geometry is prescribed by thecircular furnace wall 203K that (including the flange mount) defines adistal diameter, D_(d), for the concave spherical cap substrate 500N.The substrate 500N comprises a flange that extends between the head ofthe furnace 1801 and the burner head 503F that includes a mountingflange 228K, and the assembly is secured using fasteners 1803 orequivalent. A gas-air premixture 1802 flows axially into the inletconduit 1805 and is dispersed in the volume defined by the concavespherical cap substrate 500N and the burner head 503F. This embodimentincludes a premix flow mixing grid 1800 upstream of the combustionsubstrate 500N, which may comprise one or more of a course grid of metalfibers, plate perforations, porous heat-resistance material, or thelike, that induces turbulence in the flow to promote mixing prior to theflow passing through the pores in the combustion substrate that issufficiently porous to provide flow mixing without incurring a largepressure drop in the flow across the structure. The premix flow mixinggrid 1800 has a permeability (percentage of uncovered surface area)between about 20%, 25%, 30%, 35%, 40%, or 45% and about 50%, 55%, 60%,65%, 70%, 75%, 80%, 85%, or 90% wherein the foregoing upper and lowerbounds can be independently combined. The permeability range betweenabout 40% and about 70% is specifically mentioned. A premix flow mixinggrid with a permeability of about 60% is also specifically mentioned.The pore structure shown in the embodiment comprises a combination ofcircular 1702B and elongated 1700B pores, but any of the pore geometriesdescribe herein or their equivalents may be used, are contemplated andare considered within the scope of the claims. The gas-air premixturepenetrates the combustion substrate 500N through the pores 1700B and1702B into the combustion volume 635 circumscribed by the furnace fall203K, the combustion substrate 500N and the furnace head 1801. In thedescribed embodiment, the flame rod 502 (or, equivalently, opticalsensor) and igniter 308 penetrate transversely through the furnace wall230K, although any of the arrangements described herein or theirequivalents may be used, are contemplated and are considered within thescope of the claims.

As described above, the combustion substrate perimeter can be of anysuitable shape that is convenient to manufacture and meets the dimensionand functional requirements of the burner system. FIG. 20 illustrates anembodiment of a combustion substrate 1806 with a substrate angle equalto 90 degrees and a hexagonal perimeter comprising six edges 1808. Otherpolygonal perimeter shapes may be used depending upon the manufacturing,mounting and system requirements are contemplated and are consideredwithin the scope of the claims. A pore structure comprising circular1702D and elongated 1700D pores is shown in this embodiment, althoughany pore structure described herein or their equivalents may be used andare considered within the scope of the claims.

Another feature of the combustion substrate geometry contemplated hereinis a crease or ridge or fold in the surface of the substrate that isconvenient to manufacture and meets the dimension and functionalrequirements of the burner system. FIG. 21A illustrates an embodiment ofa combustion substrate 1811 comprising a crease or ridge or fold in thesurface 1812. This crease may be incorporated to add structural rigidityto the substrate, and/or reduce the potential for vibration when it isunder a load and supporting the combustion flame front. A pore structurecomprising circular 1702E and elongated 1700E pores is shown in thisembodiment, although any pore structure described herein or theirequivalents may be used and are considered within the scope of theclaims.

FIG. 21B shows a side view of the combustion substrate comprising aridge or crease contemplated in FIG. 21A. In the embodiment described,the ridge or crease 1812 separates the combustion substrate into twosubstantially equally-sized semi-circular half sections, although anuneven (non-equally-sized) area division is contemplated and consideredwithin the scope of the claims. The two semi-circular sections aredisposed at a crease angle, ϕ), between 0<ϕ<90°. The choice of creaseangle, ϕ), may be determined by one skilled in the art of burner designaccording to a number of design considerations including the requiredcombustion surface loading as described further below, mechanicalproperties, manufacturability constraints, potential for material stressand failure, and the resulting premix flow pattern.

The pore distribution pattern need not be uniformly distributed on thesurface of the combustion substrate. FIG. 22A shows a perspective viewof a combustion substrate 1820 with substrate angle equal to 90 degreeswith a circular perimeter 1814 comprising a pattern of pore sections1816 wherein the pores are collected. The substrate is shown withsubstrate angle equal to 90 degrees (flat plate) for ease ofillustration and discussion, but other combustion substrate geometriesdescribed here and their equivalents are contemplated and consideredwithin the scope of the claims. Shown in this embodiment are regions ofelongated 1700F and circular 1702F pores distributed in the poresections 1816. The size (area), shape and distribution of the poresections, pore dimensions and pore distribution within the sections maybe determined by one skilled in the art of burner design according to anumber of design considerations including the required combustionsurface loading as described further below, mechanical properties,manufacturability constraints, potential for material stress andfailure, and the resulting premix flow pattern. FIG. 22B shows across-sectional side view of the combustion substrate 1820 withsubstrate angle equal to 90 degrees with a circular perimeter 1814comprising a pattern of pore sections 1816 contemplated in FIG. 22A.Premix gas flow occurs from the upstream region 631, inward through thepores 1817 into the furnace combustion cavity 635 where combustionoccurs 1813.

FIG. 23A shows a perspective view of another embodiment exploiting thesame principles equivalent to the semi-cone substrate structure using apolyhedral prism, here shown a hexagonal prism comprising six triangularfaces 1826 disposed in a hexagonal prism, each pair of adjacenttriangular faces meet along one of six edges 1824. All six faces 1826and six edges 1824 meet at the peak 1828 of the hexagonal prism. Thehexagonal prism possesses a hexagonal perimeter 1822. Shown in thisembodiment are regions of elongated 1700G and circular 1702G poresdistributed in the hexagonal prism faces 1826. The pore dimensions andpore distribution within the faces 1826 may be determined by one skilledin the art of burner design according to a number of designconsiderations including the required combustion surface loading asdescribed further below, mechanical properties, manufacturabilityconstraints, potential for material stress and failure, and theresulting premix flow pattern.

FIG. 23B shows a side view of the hexagonal prism combustion substratecontemplated in FIG. 23A. Shown in this embodiment are regions ofelongated 1700H and circular 1702H pores distributed in the hexagonalprism faces 1826. The hexagonal prism has a height, H, from the basecircumscribed by the prism perimeter 1822 to the prism peak 1828.

FIG. 24A shows a perspective view of another embodiment exploiting thesame principles equivalent to the semi-cone substrate structure using aspherical cap 1830 or spherical dome, the geometrical shape formed by aportion of a sphere or of a ball cut off by a plane. The shape is alsodescribed by a spherical segment of one base of diameter D_(d), i.e.,bounded by a single plane, using the forgoing nomenclature conventions.If the plane passes through the center of the sphere, so that the heightof the cap is equal to the radius of the sphere, the spherical cap iscalled a hemisphere. The spherical cap possesses a circular perimeter1832. Shown in this embodiment are regions of elongated 1700I andcircular 1702I pores distributed on the spherical cap 1830 surface. Thepore dimensions and pore distribution within the faces may be determinedby one skilled in the art of burner design according to a number ofdesign considerations including the required combustion surface loadingas described further below, mechanical properties, manufacturabilityconstraints, potential for material stress and failure, and theresulting premix flow pattern.

FIG. 24B shows a side view of the spherical cap combustion substratecontemplated in FIG. 24A. The spherical cap possesses a peak 1831. Thespherical cap has a height, H, measured from the base circumscribed bythe spherical cap circular perimeter 1832 to the peak 1831.

FIG. 25 presents a perspective drawing showing a burner combustionsystem 1916 comprising a semi-cone shaped combustion substrate 1914. Apremix fuel-air mixture 1920 enters the burner casing 1920 through theinlet conduit 1918 and is distributed by the flow geometry in theannular region formed between the burner casing and the substrate. Themass flow of fuel-air mixture in a circumferential section 1933 of thesemi-cone combustion substrate is determined by the flow rate 1924through the distribution of pores 1922 and the surface area of thesubstrate at that altitude of the semi-cone. The volume of the burnercasing 1916, the proximal (D_(r)) and distal (D_(d)) diameters of thesemi-cone combustion substrate and the semi-cone angle, a, as measuredfrom the axis 1930 can be selected so that the fuel-air mass flow issubstantially uniform along the entire length of the substrate.

A seventh feature is that the dimensions of the combustion substrate canbe chosen such that, when a solution exists, the substrate fits withinthe overall physical constraints of the burner system whilesimultaneously providing a surface area for combustion support (loading)to provide a target burner heat production capacity. That is, achievinga prescribed burner heat production capacity requires a resulting rangeof available substrate surface area to support the combustion flamefront. The designer skilled in the art of burner design can use thegeometrical properties of the combustion substrate to achieve a targetsurface area for flame front loading while simultaneously achieving acompact configuration that fits within the physical dimension requiredby the furnace dimensions.

This feature can be illustrated using the geometry shown in FIG. 25using the right circular semi-cone combustions substrate as an examplefor simplicity. Applying known analytic geometry principles to thesemi-cone combustion substrate configuration illustrated in FIG. 25shows that the inner surface area of the substrate is given by theformula,

$\begin{matrix}{h = \frac{H \cdot D_{p}}{( {D_{d} - D_{p}} )}} & {{Eq}.\mspace{14mu} 3} \\{s = \sqrt{( \frac{D_{d}}{2} )^{2} + ( {H + h} )^{2}}} & {{Eq}.\mspace{14mu} 4} \\{A_{s} = {\pi\lbrack {( \frac{D_{d}}{2} )^{2} + {( \frac{D_{d}}{2} )s} - ( \frac{D_{p}}{2} )^{2} - {( \frac{D_{p}}{2} )\sqrt{( \frac{D_{p}}{2} )^{2} + h^{2}}}} \rbrack}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

Using the combustion semi-cone combustion substrate dimensions shown inTable 1 for illustration, FIG. 26 shows that relationship 1834 betweenthe height, H, of the substrate and the surface area, A_(s). (D_(p)=354millimeters and D_(d)=472 millimeters.) The full combustion substratesurface area, A_(s), available to support inward combustion shown inTable 1, having a design height, H=25.4 millimeters, is 134,761millimeters squared, noting that the “used” cone area in Table 1 issmaller than the full “available” cone area; thus, the cone area valuein Table 1 is 84,424.2 mm squared. As the height of the combustionsubstrate semi-cone is decreased, the available surface area decreasesuntil it reaches a minimum of 119,235 millimeters squared, correspondingto a height, H=0 where the substrate angle, α=90 degrees. (Equivalently,a flat plate.) As the height, H, increases, so does the combustionsubstrate surface area available for supporting combustion and, hence,available to increase the combustion loading and, equivalently, theburner production heat capacity. Again, the case of the semi-conecombustion substrate with substrate angle, α=90 degrees (flat plate) issimply a special case in a continuous family of substrate geometries andcorresponds to the designer choice with the minimum available combustionsurface area. Also note that the surface area loading principles are thesame for both convex and concave combustion substrate geometries.Similar area, As, and height, H, relationships can be derived forcombustion substrate geometries for the various embodiments disclosedherein and their equivalents which are contemplated by this disclosureand considered within the scope of the claims.

The inventors have also unexpectedly discovered that an inward-firingburner geometry using a composite semi-cone mesh diffuser alleviatesmany of the disadvantages known for mesh burners, particularly whenoperated in the surface combustion regime. FIG. 27 shows a cutawaydiagram of an embodiment of an inward-firing premix burner comprising asemi-cone combustion substrate and mesh insulator, although someadvantages of inward-fining premix burner embodiments discovered by theinventors are not limited to the composite semi-cone geometry. Asemi-cone shaped combustion substrate 2013 is disposed between theburner top head 2006 and the inner surface of the furnace 2030. In thisembodiment, the burner combustion substrate 2013 is a right circularfrustum wherein the proximal edge 2002 (or top edge) is a planar circleperpendicular to a longitudinal (or axial) axis 2016 with proximaldiameter D_(p) and distal edge 2036 (or bottom edge) a planar circleperpendicular to the longitudinal axis 2016 with diameter D_(d), withheight H. As in the embodiments without mesh described above, the burnercombustion substrate angle, a, in a right frustum embodiment, is thendetermined to be:

α=arctan[(D _(d) −D _(p))/H]  Eq. 6

Dimensions of the combustion substrate 213 and metal fiber mesh 2032depend upon the burner power, capacity, performance and sizerequirements of a specific application. Proximal diameters (D_(p))between 1 inch and 59 inches is specifically mentioned. Distal diameters(Dd) between 2 inches and 60 inches is specifically mentioned. Substrateheight (H) between 1 inch and 60 inches is specifically mentioned.

The semi-cone sections of the burner combustion substrate angle may haveany suitable generator angle between 1 degree, 2 degrees, 3 degrees, 4degrees, 5 degrees, 10 degrees to 11 degrees, 12 degrees, 13 degrees, 14degrees, 15 degrees, 16 degrees, 17 degrees, 18 degrees, 19 degrees, 20degrees, 21 degrees, 22 degrees, 23 degrees, 24 degrees, 25 degrees, 26degrees, 27 degrees, 28 degrees, 29 degrees, 30 degrees, 31 degrees, 32degrees, 33 degrees, 34 degrees, 35 degrees, 36 degrees, 37 degrees, 38degrees, 39 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80degrees, and 85 degrees wherein the foregoing upper and lower bounds canbe independently combined. For the right circular semi-cone, rightcircular truncated cone, and the right circular frustum, the burnercombustion substrate angles between 18 degrees and 35 degrees isspecifically mentioned. For the right circular semi-cone, right circulartruncated cone, and the right circular frustum, the burner combustionsubstrate angle of 25 degrees is also specifically mentioned.

The burner combustion substrate is porous to the flow of premix fuel-airmixtures predominately in a vapor state. Substrate pores 2012 aredistributed over the area of the burner combustion substrate 2013. Thecombustion process may be monitored by a sensor 2004 which can detect ifthe flame is extinguished.

In the embodiment shown, a premix(ed) fuel-air mixture 2010 enters theinlet 2038 of the burner and flows 2022 within a burner pre-combustioncavity 2017 and around and through the burner combustion substrate 213inward toward the longitudinal axis 2016. The fuel-air mixture 2010ratio is arranged so that the premix fuel is ignited 2020 within theburner combustion cavity 2018.

In a boiler application comprising a shell and tube heat exchanger, thecombustion products (e.g., hot gases, particulate byproducts) flow 2020towards the tubesheet 2024 where they pass through the openings 2028 ofthe heat exchanger tubes 2026. Heat generated by the combustion processis transferred across the walls of the heat exchanger tubes 2026 toproduction fluid occupying the space between the outer surfaces of thefurnace 2030 and heat exchanger tubes 2026 and the inner surface of thepressure vessel 2014, sealed at one end by the boiler top head 2008.

FIG. 28 shows a cutaway view of the diffuser 3000 comprising (in itsentirety) a right circular semi-cone combustion substrate 2012A withcircular proximal edge 2002A and distal edge 2036A. A pattern of pores(alternatively, perforations) 2013A in the combustion substrate admitthe passage of the premix fuel-air to pass 3008 from an exterior of thesubstrate, through a metal fiber mesh 2032A disposed on the substrate2012A into a interior of the diffuser 3010. The mesh 2032A is likewisein the shape of a semi-cone with proximal edge 3006 and distal edge3004.

The metal fiber mesh can be of any type or construction. Woven metalfiber (warp and weave construction), knitted, sintering techniques areall specifically mentioned, as are equivalent methods. Final mesh fabricthickness can be between 0.05″ to 0.30″, with the threads forming themesh being between 0.005 to 0.1. The threads, if used can be made fromfibers which are 0.0005 to 0.005″. If sintered metal mesh is used,fibers which are 0.0005 to 0.005″ can be used to create the sinteredmat. Joining the mesh with itself, or affixing it to a metal substrateis typically done using electric resistance spot welding, with multiplespot welds done in series to create a continuous seam where required forstrength and durability.

If an insufficient amount of diffuser (layered substrate and mesh) areais dimensioned, the flame can lift off of the mesh surface andextinguish. This is one key advantage of cavity or cone burners; thehigh blow off threshold condition supports flame stability in bothsurface and SF combustion and, as a result, can potentially reduce theamount of surface area needed in comparison with other alternatives,thereby enhancing compactness of the apparatus and reduce materialrequirements in the manufacturing process.

There are several important advantages to the arrangements in thedisclosed embodiments incorporating a mesh diffuser. A first aspect ofthe embodiment incorporating a mesh diffuser is that the mesh insulationlayer enables the premix fuel-air burner combustion system to beoperated in the “surface combustion” regime where the mass flow ratethrough the diffuser is low. In the absence of a mesh insulating layer,the close proximity of the flame front to the substrate can result inexcessively high temperatures of the substrate, which can lead tothermal stresses and material failure. Additionally, these hightemperatures can ultimately exceed autoignition temperature for premixedfuel and air, resulting the flame igniting behind the substrate, causingcombustion in the annular region between the burner casing andsubstrate.

A second aspect of the embodiment incorporating a mesh diffuser is thatthe metal fiber mesh distributes and homogenizes the premix fuel-airflow stream emanating through the substrate pores or perforations, andcontributes to a more uniform distribution of fuel on the combustiondiffuser surface. Moreover, the mesh serves to further direct thepassage of the premix fuel-air flow stream so that it emerges close toorthogonal to the inner diffuser surface (also called flowstratification), further creating a uniform fuel stream for the surfacecombustion process.

A third aspect of the embodiment incorporating a mesh diffuser is thatthe action of the metal fiber mesh to distribute and direct the premixfuel-air mixture to produce a uniform flow field for surface combustionreduces the risk of flashback. That is, it reduces the risk that theflame front locally migrates from the interior combustion surface,through the pores in the substrate, and into the annular region betweenthe burner casing and the substrate.

A fourth aspect of the embodiment incorporating a mesh diffuser is thatfine control of the delivery of the premix fuel-air to the interior ofthe burner cavity, or the burner combustion cavity, by the metal fibermesh implies that the pores or perforations in the combustion substratecan be coarser and less uniform than if the substrate pores were solelyresponsible for the diffusion of the fuel mixture. Thus, theincorporation of the metal fiber mesh disposed on the inner substratesurface relaxes the manufacturing requirements and tolerances for thecombustion substrate, reducing cost and enabling a broader range ofusable materials and fabrication methods.

For example, conventional fabrication methods that stamp or punch holesin sheet metal to for the combustion substrate in a uniform pattern mayproduce a non-uniform radial pattern in a semi-cone element. This wouldbe problematic if the substrate is used alone since it would result in anon-uniform radial distribution of premix fuel-air to the combustionprocess. (More flow where the pores are larger or denser; less flow indirections where the pores are smaller or sparser.) However, theaddition of the metal fiber mesh layer serves to redistribute the flowevenly through the uniform mesh openings.

A fifth aspect of the embodiment incorporating a mesh diffuser is thatin some embodiments where the premix fuel-air mixture is generated byinjecting fuel into an air stream before it reaches the burner inletconduit 238, the mesh helps provides additional mixing through theturbulent action of the fuel stream passing through the mesh openings.Thus, the metal fiber mesh contributes to the creation of a well-mixedlean fuel-air stream before it is ignited in the surface combustionprocess.

The various components of the premix fuel burner combustion system caneach independently comprise any suitable material. Use of a metal isspecifically mentioned. Representative metals include iron, aluminum,magnesium, titanium, nickel, cobalt, zinc, silver, copper, and an alloycomprising at least one of the foregoing. Representative metals includecarbon steel, mild steel, cast iron, wrought iron, a stainless steelsuch as a 300 series stainless steel or a 400 series stainless steel,e.g., 304, 316, or 439 stainless steel, Monel, Inconel, bronze, andbrass. Specifically mentioned is an embodiment in which the premix fuelburner combustion system components each comprise steel, specificallystainless steel. The premix burner combustion system may comprise aburner head, a combustion substrate, a baffle, a furnace wall that caneach independently comprise any suitable material. Use of a steel, suchas mild steel or stainless steel this mentioned. While not wanting to bebound by theory, it is understood that use of stainless steel in thedynamic components can help to keep the components below theirrespective fatigue limits, potentially eliminating fatigue failure as afailure mechanism, and promote efficient heat exchange.

The disclosed system can alternately comprise, consist of, or consistessentially of, any appropriate components herein disclosed. Thedisclosed system can additionally be substantially free of anycomponents or materials used in the prior art that are not necessary tothe achievement of the function and/or objectives of the presentdisclosure.

Embodiments Further Disclosed

Embodiment A: Further disclosed is a premix burner comprising: a burnercasing with an inlet conduit for a premix fuel-air mixture to bedisposed in the burner casing; a porous burner combustion substratedisposed in the burner casing wherein a premix fuel-air mixture entersthe inlet conduit on an outside (exterior) of the burner combustionsubstrate. A premix fuel-air mixture is disposed under pressure throughthe burner inlet to an outside of the porous burner combustionsubstrate; passes through pores in the burner combustion substrate to aninterior of the substrate; the fuel-air mixture is ignited in theinterior of the burner combustion substrate; combustion gases andproducts flow from the interior of the burner combustion substratethrough an outlet in the burner casing.

Embodiment B: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of acylinder.

Embodiment C: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of acomposite semi-cone.

Embodiment D: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of asemi-cone.

Embodiment E: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of atruncated cone.

Embodiment F: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of acircular truncated cone.

Embodiment G: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of a rightcircular truncated cone.

Embodiment H: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of afrustum.

Embodiment I: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of acircular frustum.

Embodiment J: Further disclosed is the premix burner of Embodiment A,wherein the porous burner combustion substrate has the shape of a rightcircular frustum.

Embodiment K: Further disclosed is the premix burner of any ofEmbodiments A to J, further comprising a plurality of burner casinginlets disposed on the burner casing.

Embodiment L: Further disclosed is a premix burner of any of theEmbodiments A to K, wherein the semi-cone generator angle is ninetydegrees.

Embodiment M: Further disclosed is a premix burner comprising: a burnercasing with an inlet conduit for a premix fuel-air mixture to bedisposed in the burner casing; a porous burner combustion substratedisposed in the burner casing; a metal fiber mesh disposed on theinterior surface of the combustion substrate; wherein a premix fuel-airmixture enters the inlet conduit on an outside (exterior) of the burnercombustion substrate. A premix fuel-air mixture is disposed underpressure through the burner inlet to an outside of the porous burnercombustion substrate; passes through pores in the burner combustionsubstrate and through the pores of the metal fiber mesh to an interiorof the diffuser; the fuel-air mixture is ignited in the interior of theburner combustion substrate; combustion gases and products flow from theinterior of the burner cavity through an outlet in the burner casing.

Embodiment N: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a cylinder.

Embodiment O: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a composite semi-cone.

Embodiment P: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a semi-cone.

Embodiment Q: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a truncated cone.

Embodiment R: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a circular truncated cone.

Embodiment S: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a right circular truncated cone.

Embodiment T: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a frustum.

Embodiment U: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a circular frustum.

Embodiment V: Further disclosed is the premix burner of Embodiment M,wherein the porous burner combustion substrate and metal fiber mesh hasthe shape of a right circular frustum.

Embodiment W: Further disclosed is the premix burner of any ofEmbodiments M to V, further comprising a plurality of burner casinginlets disposed on the burner casing.

Embodiment X: An inward-firing surface combustion burner, comprising: aburner casing configured to receive a fuel-air mixture at a burner inletand to provide hot combustion gas at a burner output; a combustionsubstrate disposed within the burner casing, the substrate having ashape comprising at least a semi-cone, having a substrate angle measuredfrom a longitudinal axis, having a substrate porosity defined by aplurality of pores, and having a substrate inner surface and a substrateouter surface; a mesh disposed on the inner surface of the combustionsubstrate; the substrate configured to receive the fuel-air mixture atthe outer surface of the substrate, the fuel-air mixture passing throughthe pores of the substrate and through the pores of the mesh at amixture flow rate from the substrate outer surface toward the substrateinner surface; the burner configured such that, in operation, thefuel-air mixture ignites directly upon or largely in contact with theplurality of pores of the mesh.

Embodiment Y: The burner of Embodiment X, wherein the substrate anglehas a range of values from 1 degree to 89 degrees.

Embodiment Z: The burner of Embodiment X, wherein a volume of the burnercasing, a proximal diameter (D_(p)) of the substrate, a distal diameter(D_(d)) of the substrate, and a semi-cone angle of the substrate, areset such that the mixture rate is substantially uniform along a lengthof the substrate and forms a substantially uniform flame front along theinner surface of the substrate.

Embodiment AA: The burner of Embodiment X, wherein the surfacecombustion process provides a substantially uniform temperaturedistribution across the substrate inner surface and provides asubstantially uniform flow field distribution of the hot combustion gasat the burner output.

Embodiment BB: The burner of Embodiment X, wherein the substratecomprises a plurality of porous layers to create the substrate porosity.

Embodiment CC: The burner of Embodiment X, wherein the shape of thesubstrate comprises at least one of: cone, semi-cone, compositesemi-cone, truncated cone, frustum, right frustum, right circulartruncated cone, and a right circular frustum.

Embodiment DD: The burner of Embodiment X, wherein the pores have ashape comprising at least one of: circular, rectangular, symmetricalshape, and asymmetrical shape.

Embodiment EE: The burner of Embodiment X, further comprising an ignitordisposed on an inner side of the substrate where the surface combustionoccurs.

Embodiment FF: The burner of Embodiment X, wherein the combustionsubstrate comprises a proximal diameter (D_(p)) about 1 to 59 inches, adistal diameter (D_(d)) between 1 and 60 inches, a substrate height (H)between 1 and 60 inches, and a substrate angle between 1 degree and 89degrees.

Embodiment GG: An inward-firing surface combustion burner, comprising: aburner casing configured to receive a fuel-air mixture at a burner inletand to provide hot combustion gas at a burner output; a combustionsubstrate disposed within the burner casing, the substrate having ashape comprising at least a semi-cone, having a substrate angle measuredfrom a longitudinal axis, having a substrate porosity defined by aplurality of pores, and having a substrate inner surface and a substrateouter surface; a mesh disposed on the inner surface of the combustionsubstrate; the substrate configured to receive the fuel-air mixture atthe outer surface of the substrate, the fuel-air mixture passing throughthe pores of the substrate and through the pores of the mesh at amixture flow rate from the substrate outer surface toward the substrateinner surface; the burner configured such that, in operation, thefuel-air mixture ignites directly upon or largely in contact with theplurality of pores of the mesh, such that surface combustion occurs.

Further disclosed is a hydronic fluid heating system (equivalently, a“hydronic boiler”) comprising a premix combustion system of any ofEmbodiments A to GG or elsewhere disclosed in this specification.

Further disclosed is a steam fluid heating system (equivalently, a“steam boiler”) comprising a premix combustion system of any ofEmbodiments A to GG or elsewhere disclosed in this specification.

Further disclosed is a thermal fluid heating system (equivalently, a“thermal fluid boiler”) comprising a premix combustion system of any ofEmbodiments A to GG or elsewhere disclosed in this specification.

Further disclosed is a packaged burner comprising a premix combustionsystem of any of Embodiments A to GG or elsewhere disclosed in thisspecification.

The disclosed system can alternately comprise, consist of, or consistessentially of, any appropriate components herein disclosed. Thedisclosed system can additionally be substantially free of anycomponents or materials used in the prior art that are not necessary tothe achievement of the function and/or objectives of the presentdisclosure.

The terms “a” and “an” do not denote a limitation of quantity, butrather denote the presence of at least one of the referenced item. Theterm “or” means “and/or” unless clearly indicated otherwise by context.Reference throughout the specification to “an embodiment”, “anotherembodiment”, “some embodiments”, and so forth, means that a particularelement (e.g., feature, structure, step, or characteristic) described inconnection with the embodiment is included in at least one embodimentdescribed herein, and may or may not be present in other embodiments. Inaddition, it is to be understood that the described elements may becombined in any suitable manner in the various embodiments. “Optional”or “optionally” means that the subsequently described event orcircumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not. Theterms “first,” “second,” and the like, “primary,” “secondary,” and thelike, as used herein do not denote any order, quantity, or importance,but rather are used to distinguish one element from another. The terms“front”, “back”, “bottom”, and/or “top” are used herein, unlessotherwise noted, merely for convenience of description, and are notlimited to any one position or spatial orientation.

The endpoints of all ranges directed to the same component or propertyare inclusive of the endpoints, are independently combinable, andinclude all intermediate points. For example, ranges of “up to 25 N/m,or more specifically 5 to 20 N/m” are inclusive of the endpoints and allintermediate values of the ranges of “5 to 25 N/m,” such as 10 to 23N/m.

Unless defined otherwise, technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart to which this invention belongs.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety. However, if a termin the present application contradicts or conflicts with a term in theincorporated reference, the term from the present application takesprecedence over the conflicting term from the incorporated reference.

As will be recognized by those of ordinary skill in the pertinent art,numerous modifications and substitutions can be made to theabove-described embodiments of the present disclosure without departingfrom the scope of the disclosure. Accordingly, the preceding portion ofthis specification is to be taken in an illustrative, as opposed to alimiting, sense.

Although the disclosure has been described herein using exemplarytechniques, algorithms, or processes for implementing the presentdisclosure, it should be understood by those skilled in the art thatother techniques, algorithms and processes or other combinations andsequences of the techniques, algorithms and processes described hereinmay be used or performed that achieve the same function(s) and result(s)described herein and which are included within the scope of the presentdisclosure. In addition, unless otherwise recited herein, any embodimentdisclosed herein may be used with any other embodiment disclosed herein.

Any process descriptions, steps, or blocks in process or logic flowdiagrams provided herein indicate one potential implementation, do notimply a fixed order, and alternate implementations are included withinthe scope of the preferred embodiments of the systems and methodsdescribed herein in which functions or steps may be deleted or performedout of order from that shown or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved, as would be understood by those reasonably skilled in the art.

It is noted that the Figures are to be taken as an illustrative exampleonly, and are not to scale.

All cited references are incorporated in their entirety to the extentneeded to understand the present disclosure, and to the extent permittedby applicable law.

It should be understood that, unless otherwise explicitly or implicitlyindicated herein, any of the features, characteristics, alternatives ormodifications described regarding a particular embodiment herein mayalso be applied, used, or incorporated with any other embodimentdescribed herein.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments could include, but do not require, certain features,elements, or steps. Thus, such conditional language is not generallyintended to imply that features, elements, or steps are in any wayrequired for one or more embodiments or that one or more embodimentsnecessarily include logic for deciding, with or without user input orprompting, whether these features, elements, or steps are included orare to be performed in any particular embodiment.

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present disclosure.

What is claimed is:
 1. A combustion burner, comprising: a burner casingconfigured to receive a fuel-air mixture at a burner inlet and toprovide hot combustion gas at a burner output; a combustion substratedisposed within the burner casing, the substrate having a shape that issubstantially flat, having a substrate porosity defined by a pluralityof pores, the pores having a 3D shape comprising a predeterminedthickness, and having a substrate inner surface and a substrate outersurface; the substrate configured to receive the fuel-air mixture at theouter surface of the substrate, the fuel-air mixture passing through thepores at a mixture flow rate from the substrate outer surface toward thesubstrate inner surface; the burner configured such that, in operation,the fuel-air mixture ignites in a reaction zone inside a combustioncavity near the plurality of pores to form a respective plurality offlamelets, each flamelet corresponding to one of the pores, wherein theplurality of flamelets exhibits suspended flame combustion (SFcombustion); and wherein the porosity is set such that a flameequilibrium ratio (ρ) causes the reaction zone, for 1<ρ<100, to beapproximately stationary and inside the combustion cavity.
 2. The burnerof claim 1, wherein the 3-dimensional structure of the pores are setsuch that the mixture rate is substantially uniform along a length ofthe substrate and the plurality of flamelets forms a stablesubstantially uniform flame front along the inner surface of thesubstrate.
 3. The combustion burner of claim 1 wherein at least one ofthe pores comprises a 3-D shape of a nozzle.
 4. The combustion burner ofclaim 1, wherein the thickness of at least one of the pores is thethickness of 20 GA steel (about 0.9525 mm).
 5. The burner of claim 1,wherein the 3-dimensional structure of the pores is set such that theplurality of flamelets exhibits stable suspended flame combustion (SFcombustion).
 6. The burner of claim 1, wherein the 3-dimensionalstructure of the pores are set such that the mixture rate issubstantially uniform along a length of the substrate and the pluralityof flamelets forms a stable substantially uniform flame front along theinner surface of the substrate.
 7. The burner of claim 1, furthercomprising a mesh disposed on the substrate, and wherein the thicknessof the pores is determined by a combined thickness of the mesh and thesubstrate.
 8. The burner of claim 1, wherein the 3-dimensional structureof the pores have a shape comprising at least one of: circular,rectangular, symmetrical shape, and asymmetrical shape, and having thepredetermined thickness.
 9. The burner of claim 1, wherein the shape ofat least one pore is an approximately circular shape having a maximumdiameter between about 0.5 millimeters and about 2 millimeters and thepredetermined thickness is at least 0.9525 mm.
 10. The burner of claim1, wherein the shape of at least one of the pores is an approximatelyslot shape with width between about 0.5 millimeters and about 2millimeters and length between about 2 millimeters and about 15millimeters and the predetermined thickness is at least 0.9525 mm.